1. Field of the Invention
The present invention relates to surveying instruments and methods of analyzing measuring data.
2. Brief Description of Related Art
A conventional surveying apparatus, such as a total-station, a tacheometer, and a theodolite, comprise an optical system, such as a telescope, having a predetermined optical axis carried on a mounting structure such as a tripod. A user, while looking through the telescope, adjusts an orientation of the telescope relative to the tripod such that a target of interest coincides with the optical axis of the telescope. The target of interest may comprise a reflector or pole or other features of an object such as an edge of a building or a landmark or others. By measuring the angle of the telescope relative to the mounting structure, it is possible to determine a position of the target. For this purpose, the surveying apparatus may comprise angle sensors, an optical distance measuring system and a light projection system transmitting a light beam through the telescope to a reflector located at the target.
Recently, research has been performed to develop a surveying apparatus comprising a camera for detecting an image of a scenario including the target, wherein an image processing is performed to automatically identify the target within the image and to determine the position of the target within the image.
It has been found that the conventional methods of image processing may not always achieve a satisfactory measuring result. The images detected by the camera are subject to disturbances due to varying lighting conditions. Moreover, the object to be identified in the image may have complex structures due to textured surfaces and image backgrounds, and portions of the objects to be identified may be hidden by other objects, such as trees. Therefore, a reliable and robust detection of object features is not always possible.